Handle invalid RFC 1964 tokens [CVE-2014-4341...]

Detect the following cases which would otherwise cause invalid memory
accesses and/or integer underflow:

* An RFC 1964 token being processed by an RFC 4121-only context
  [CVE-2014-4342]

* A header with fewer than 22 bytes after the token ID or an
  incomplete checksum [CVE-2014-4341 CVE-2014-4342]

* A ciphertext shorter than the confounder [CVE-2014-4341]

* A declared padding length longer than the plaintext [CVE-2014-4341]

If we detect a bad pad byte, continue on to compute the checksum to
avoid creating a padding oracle, but treat the checksum as invalid
even if it compares equal.

CVE-2014-4341:

In MIT krb5, an unauthenticated remote attacker with the ability to
inject packets into a legitimately established GSSAPI application
session can cause a program crash due to invalid memory references
when attempting to read beyond the end of a buffer.

    CVSSv2 Vector: AV:N/AC:M/Au:N/C:N/I:N/A:P/E:POC/RL:OF/RC:C

CVE-2014-4342:

In MIT krb5 releases krb5-1.7 and later, an unauthenticated remote
attacker with the ability to inject packets into a legitimately
established GSSAPI application session can cause a program crash due
to invalid memory references when reading beyond the end of a buffer
or by causing a null pointer dereference.

    CVSSv2 Vector: AV:N/AC:M/Au:N/C:N/I:N/A:P/E:POC/RL:OF/RC:C

[tlyu@mit.edu: CVE summaries, CVSS]

(cherry picked from commit fb99962)

ticket: 7949
version_fixed: 1.12.2
status: resolved

src/lib/gssapi/krb5/k5unseal.c

@@ -74,6 +74,7 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer,
     int conflen = 0;
     int signalg;
     int sealalg;
+    int bad_pad = 0;
     gss_buffer_desc token;
     krb5_checksum cksum;
     krb5_checksum md5cksum;
@@ -86,25 +87,31 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer,
     krb5_ui_4 seqnum;
     OM_uint32 retval;
     size_t sumlen;
+    size_t padlen;
     krb5_keyusage sign_usage = KG_USAGE_SIGN;
 
     if (toktype == KG_TOK_SEAL_MSG) {
         message_buffer->length = 0;
         message_buffer->value = NULL;
     }
 
-    /* get the sign and seal algorithms */
-
-    signalg = ptr[0] + (ptr[1]<<8);
-    sealalg = ptr[2] + (ptr[3]<<8);
-
     /* Sanity checks */
 
-    if ((ptr[4] != 0xff) || (ptr[5] != 0xff)) {
+    if (ctx->seq == NULL) {
+        /* ctx was established using a newer enctype, and cannot process RFC
+         * 1964 tokens. */
+        *minor_status = 0;
+        return GSS_S_DEFECTIVE_TOKEN;
+    }
+
+    if ((bodysize < 22) || (ptr[4] != 0xff) || (ptr[5] != 0xff)) {
         *minor_status = 0;
         return GSS_S_DEFECTIVE_TOKEN;
     }
 
+    signalg = ptr[0] + (ptr[1]<<8);
+    sealalg = ptr[2] + (ptr[3]<<8);
+
     if ((toktype != KG_TOK_SEAL_MSG) &&
         (sealalg != 0xffff)) {
         *minor_status = 0;
@@ -153,6 +160,11 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer,
         return GSS_S_DEFECTIVE_TOKEN;
     }
 
+    if ((size_t)bodysize < 14 + cksum_len) {
+        *minor_status = 0;
+        return GSS_S_DEFECTIVE_TOKEN;
+    }
+
     /* get the token parameters */
 
     if ((code = kg_get_seq_num(context, ctx->seq, ptr+14, ptr+6, &direction,
@@ -207,7 +219,20 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer,
         plainlen = tmsglen;
 
         conflen = kg_confounder_size(context, ctx->enc->keyblock.enctype);
-        token.length = tmsglen - conflen - plain[tmsglen-1];
+        if (tmsglen < conflen) {
+            if (sealalg != 0xffff)
+                xfree(plain);
+            *minor_status = 0;
+            return(GSS_S_DEFECTIVE_TOKEN);
+        }
+        padlen = plain[tmsglen - 1];
+        if (tmsglen - conflen < padlen) {
+            /* Don't error out yet, to avoid padding oracle attacks.  We will
+             * treat this as a checksum failure later on. */
+            padlen = 0;
+            bad_pad = 1;
+        }
+        token.length = tmsglen - conflen - padlen;
 
         if (token.length) {
             if ((token.value = (void *) gssalloc_malloc(token.length)) == NULL) {
@@ -403,7 +428,7 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer,
 
     /* compare the computed checksum against the transmitted checksum */
 
-    if (code) {
+    if (code || bad_pad) {
         if (toktype == KG_TOK_SEAL_MSG)
             gssalloc_free(token.value);
         *minor_status = 0;

src/lib/gssapi/krb5/k5unsealiov.c

@@ -69,7 +69,14 @@ kg_unseal_v1_iov(krb5_context context,
         return GSS_S_DEFECTIVE_TOKEN;
     }
 
-    if (header->buffer.length < token_wrapper_len + 14) {
+    if (ctx->seq == NULL) {
+        /* ctx was established using a newer enctype, and cannot process RFC
+         * 1964 tokens. */
+        *minor_status = 0;
+        return GSS_S_DEFECTIVE_TOKEN;
+    }
+
+    if (header->buffer.length < token_wrapper_len + 22) {
         *minor_status = 0;
         return GSS_S_DEFECTIVE_TOKEN;
     }